REP-0127: add <depend> element to package.xml
REP-0127: remove <depend> element from package.xml format 1 description
REP-0127: clarifications and corrections preparing for acceptance review
REP-0127: minor improvements

format according to REP-0012
use ".. warning" instead of ".. todo" due to github rendering limitations
clarify wording in places
REP-0127: updates from internal review comments
REP-0127: clean up references
REP-0127: fix error in example package.xml
Merge pull request #56 from jack-oquin/master

REP-0127: clarifications and corrections preparing for acceptance review